Of all the additional modes (i.e. apart from traditional 2 channel or 2.1 channel) in the 990, the one that I like most for music is DTS NEO-6 (albeit I like to turn the surrounds down by about 4 dB or so to make its sound more natural). I find this to be the least gimmicky (and therefore most musical) of the modes and have the least detrimental effect on the bass.

However, that's when I feel like listening to the source material in a slightly different way; Doug917 makes a very good point - when the source material is good (and was likely engineered with 2 channel in mind), and as the 990 seems to handle that well (digitally) it's tough to leave that.

In short I'd say I use 2.1 mode for 95% of my traditional 2-channel listening, and DTS NEO-6 (with surrounds throttled back a little) for something different.

Mark